Uncertainty concerning the return of migratory birds

[19 January 2006 - 00h00]
[mis à jour le 3 July 2007 à 18h01]

South-East Asia, Siberia, Russia, Turkey… the bird flu virus is currently moving in the same direction as migratory bird flows. Specialists are paying particular attention in France. Surveillance of migratory birds has been stepped up in several key sites in the country, such as the Lac de Grand-Lieu in the Nantes region, on the Atlantic coast just south of Brittany.

The thermometer stood at 3 degrees below zero this January morning, just a few kilometres south of Nantes, the 6th largest city in France. The Lac de Grand-Lieu, like a peaceful predator, holds a thick mist within its grasp. It was to remain all day. Christophe Sorin and Alain Caizergues are used to this. They take out the boat anyway, heading for the wide open lake.

Three minutes later and 1.6 km out from the shore, there is the first hoop net. Four of those are spread out over the 7 000 hectares covered by the lake in winter. They remove a few pochard ducks. Some have rings, others do not. They then release the dozen or so struggling coots.

Christophe Sorin is a technician at the “Loire-Atlantique Hunting Federation”. Alain Caizergues is an engineer-researcher at the National Wild Fauna and Hunting Office, the ONCFS, a satellite body of the Ministry of Agriculture and Fisheries.

Both men are veritable sentinels, essential links in the surveillance chain of migratory birds in France, the SAGIR network. An essential chain given that bird flu started in Asia, arrived at the Urals and came to Turkey, along with the migratory flows.

For the past few weeks, the two men have been increasing the daily catches. The aim is to identify as early as possible any risk of the appearance of the H5N1 virus in France. That morning they bring back about twenty ducks which are examined and from which a few samples are taken before they are released again. This time a female pochard duck has her head stuck into a canvas bag. The darkness prevents stress. Equipped with protective gloves and glasses, the two men measure the length of the legs, before weighing the duck and placing a ring on her. Then her beak is stamped, painlessly, with the number 51.

Anticipating the risk of the virus migrating…

Next, “we take a sample of droppings to look for H5N1”, explains Alain Caizergues. The hypothesis is that if a bird is infected, its excrement may contaminate others, simply via the respiratory system or through contact with soiled feathers.

Like the Camargue area, the Lac de Grand-Lieu, one of the biggest ornithological reserves in Europe, is currently the focus of all eyes. According to the experts, the risk of an epizootic, in other words an epidemic affecting animals, will be higher around the end of February. This period marks the return to our regions of birds that left to spend the winter in the warmth of Africa.

But down there they crossed the paths of other birds in exile, this time from Asia and the Urals, regions that are infected with H5N1. Jean-Roch Gaillet, Director of Health Measures at the ONCFS, confirms that “Africa is currently a meeting zone for birds from infected regions and from our regions. Our birds coming back in the spring risk bringing the disease with them.”

To anticipate this risk, French teams from the ONCFS and the CIRAD, the International Centre for Agronomic Research and Development, are currently in Africa to observe the situation. And to take samples of droppings. Three large migratory basins are being closely monitored: the basin of Lake Chad, the internal delta of the Niger and the Senegal delta, on the border between this country and Mauritania. The risk of the virus migrating to France and Europe will possibly be reviewed on the basis of this analysis. Either upwards or downwards.

A number of European countries have anticipated this risk. France, for instance, which has decided to confine poultry in several departments. But researchers are particularly concerned about wild birds and several species that are very resistant to the H5N1 virus, such as the mallard. Measures have already been taken to cope with an epizootic. Should a case of bird flu emerge on a French farm, the herd will be confined and then slaughtered.

Persistent fear of a mutation

Apart from the epizootic itself, the spread of the infection among birds is increasing the risk of direct infection of man, which essentially occurs during close and frequent contact with the respiratory secretions and excrement of infected animals.

But the scenario most feared by the World Health Organization is the mutation of the H5N1 virus in the event that it should combine with the human flu virus. As recently confirmed to us by Dr Guénaël Rodier, Special Adviser responsible for Communicable Diseases at the WHO Regional Office for Europe in Copenhagen, “the more cases of seasonal human flu there are, the more chance there is of the H5N1 virus recombining”.

That is why the WHO is paying special attention to ensuring that the “mass and rapid slaughter of infected poultry, which is the first line of defence of international public health”, is carried out under quite specific sanitary conditions. A mutation of the virus could very well emerge during the slaughter. For instance if someone has the flu and is not protected with appropriate clothing and equipment: especially gloves and masks.

This scenario is all the more feared because no vaccine will be immediately available to combat the new virus that would then appear. This would pave the way for a pandemic, in other words an epidemic on a world scale...

No risk from food

Humans cannot be contaminated by H5N1 through food. For two reasons: first, heating food at 70°C for a few minutes destroys the virus. A chicken is usually cooked in the oven at 180°C or even 200°C. Second, the acidity of the stomach can destroy the bird flu virus.

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